400ZR is an implementation agreement from the Optical Internetworking Forum (OIF) for high bandwidth data center interconnects via optical modules. This implementation agreement specifies an interoperable digital coherent 400ZR interface targeted at short-reach (80 km or more) Dense Wavelength Division Multiplexing (DWDM) amplified noise limited links and unamplified loss limited links. 400ZR specifies framing techniques and will be embodied in pluggable optical modules such as an Octal Small Form-factor Pluggable (OSFP) or Double Density Quad Small Form-factor Pluggable (QSFP-DD). Effectively, 400ZR provides a new type of Ethernet PHY based on optical coherent technology. 400ZR reduces cost and complexity for high bandwidth data center interconnects using higher-order modulation and DWDM while ensuring coordination at both ends eliminating proprietary vendor solutions. Pluggable coherent 400ZR solutions support 400 G Ethernet client only and multi-vendor interoperability. With industry-wide collaboration on 400ZR, the derivative term ‘ZR+’ is being used as a catch-all reference covering the expanded use of footprint-optimized, longer-reach, multi-rate (>200 G) pluggable solutions in next-generation data center interconnects and metro networks.
It is expected ZR and ZR+ will be widely deployed in data center interconnects and metro networks. However, the current scope of such work focuses on single client transport. There is a large amount of 100 Gigabit Ethernet (GbE) services deployed, and the transition to 400ZR native rates (400 GbE) will be gradual. There is a need to provide a technique for multiplexing non-standard rates or subrating with ZR and ZR+, for example, support of 3×300 GbE into one coherent 300ZR+ interface.